Process for treating titanium metal



nited 2,864,690 PROCESS FOR TREATING TITANIUM METAL No Drawing.Application March 8, 1955 Serial No. 493,067

8 Claims. (Cl. 75--84.4)

This invention relates in general to the treatment of refractory metaland in particular to a method for leaching impure titanium metal. Stillmore specifically the invention relates to an improved method forremoving from titanium metal contaminants which may be present or whichmay be formed as by-products in the titanium metal during the productionthereof such as, for example, magnesium metal and/or various watersoluble or acid soluble compounds such as magnesium chloride and thelike; the instant application being a continuation-in-part of ourapplications Serial No. 365,776, Serial No. 365,777 and Serial No.365,778, all of which were filed July 2, 1953 and expressly abandoned onApril 27, 1955.

When titanium metal is produced by a process such as that described, forexample in U. S. Patent No. 2,205,854 wherein titanium tetrachloride andan active reducing metal such as magnesium metal are reacted at elevatedtemperatures to form titanium metal and a chloride salt of the reducingmetal, the crude titanium metal which is formed is usually contaminatedwith by-products such as, for example, the chloride salt of the reducingmetal and the reducing metal itself. Before the crude titanium metal canbe further utilized in the various commercial applications for which itmay be suitable, it is necessary for such contaminant or by-products tobe separated from the titanium metal by means 'of a leaching operation.In removing such contaminants, the titanium metal is first subdividedand then leached with water or a dilute acid solution as the leachingmedium. It is possible through the employment of proper water leachingprocedures to effectively remove substantially all of the water solubleimpurities such as for example, magnesium chloride, and by employing adilute acid in the leaching step it is further possible to remove themetallic impurities such as magnesium metal as well as the solublesalt-like compounds. Because of the economics involved it has generallybeen the practice to use an acidic solution of for example, hydrochloricor dilute sulphuric acid in such leaching operations. However, insubsequent methods of processing and in particular the step of meltingthe leached titanium metal by for example, an arc melting operation inorder to cast it into suitable forms for commercial utilization, it hasbeen observed that often undesirable ditficulties have been encountered,and that for some reason the titanium metal product is not amenable toare melting procedures. The reason for this are not clear; however, itis possible that after the dilute acid leaching operation the titaniummetal product may contain some absorbed gas such as 'for example,hydrogen, and that the absorbed gaseous material is released during thesubsequent arc melting operation. Such action results in the loss of arcstability and in the spattering of metal which is observed and whichdoes not permit a satisfactory arc melting operation to be obtained.

Accordingly, an object of this invention is to provide a satisfactorymethod for removing by-products from impure titanium metal. Anotherobject is to provide a tent 2,864,690 Patented Dec. 16, 1953 crudetitanium metal to render said metal amenable to arc melting whichcomprises leaching said crude titanium metal with an inorganic oxidizingacid solution. It has been found that leaching sub-divided crudetitanium metal, produced by reduction of its halide and containingreaction by-products, with an oxidizing acid solution according to theinstant invention prevents hydrogen from being absorbed into the metalduring leaching thereby producing a superior type of ductile titaniummetal. Substantially any inorganic oxidizing acid in aqueous solutionwhich is capable of oxidizing hydrogen gas to hydrogen ion in an acidsolution may be successfully employed. Among the oxidizing agents. whichhave been successfully used are nitric acid and acid solutions ofnitrate salts, ferric salts, Na CrO K Cr O KMnO H 0 NaClO NaClO, NaClO,,KBrO K10 TiCl MnO PbO SnCl CuSO and oxidizing gases such as chlorine,oxygen, ozone and bromine.

In carrying out the instant invention the oxidizing agent is usuallydissolved in an acidic solution. Some of these agents, however, are onlyvery slightly soluble, particularly gases such as oxygen, and ozone. Inthese inslances it is desirable to add these gases by bubbling themthrough the solution during the leaching operation. In the case ofchlorine and other gases the gas may be bubbled through the solution orformed in situ in some manner in the solution itself. Since some of thesalts used as oxidizing agents are only slightly soluble in the acidsolution, it is desirable although not essential to control the rate ofaddition of either the oxidizing agent or the acid portion of thesolution.

It is obvious that the specific quantities of oxidizing agents to beemployed in any particular operation will depend upon a variety offactors such as for example, the type of oxidizing agent to be employed,the amount of contamination which may be present, the physical form ofthe titanium metal product to be purified and other operationalvariations.

Preferably sufiicient oxidizing agent should be present in the leachingsolution to react with at least a major portion of the hydrogen whichtheoretically would be released if the oxidizing agent were not employedin the leaching solution. An excess over this amount may be employed toinsure superior results. In most cases it has been found thatsatisfactory results are obtained when at least 0.5% of an oxidizingagent up to the maximum solubility, based on the weight of the leachingsolution, is employed. Preferably from about 0.5 to about 20% of anoxidizing agent should be employed and in the case of HNO amounts ashigh as 70% may be employed.

Typical of a leaching solution comprising an acid and an inorganicoxidizing agent is a ferric iron containing acidic solution consistingessentially of a mineral acid such as hydrochloric acid or sulfuric acidand a ferric compound such as ferric chloride. Other ferric solutions ofmineral acids which have been found particularly suitable for employmentaccording to the instant invention include ferric sulfate, ferricnitrate, ferric phosphate, ferric ammonium sulfate and the like. Forsatisfactory operations it has been found that it is preferably toemploy from about 2.0% to maximum solubility of the ferric compound, andpreferably from about 2% to about 20%.

01. o th pre erred em odiments of the in t nt invention is to employ anitrate-containing acidic solution as the leaching agent. The termnitrate-containing herein employed is used in the obvious sense toinclude solutions which contain the N grouping such as nitric acid,sodium nitrate, potassium nitrate and the like. The solution may ofcourse be nitric acid alone or any acidic solution containing nitratecompounds. Any nitrate-containing solution sufficiently acidic to attackfor example, magnesium metal, may be suitably employed. Obviously asolution of nitric acid is sufliciently acidic in its own right; howeveran aqueous solution of sodium nitrate is usually considered to beneutral, and thus it would be necessary in addition to have present anacidic material such as hydrochloric acid, sulphuric acid, acetic acid,or some salt such as magnesium chloride which forms an acceptable acidicsolution, capable of dissolving metallic magnesium. It is to beappreciated that mineral and organic acids other than those abovementioned may also be employed. 7

According to a preferred embodiment of the instant invention the amountof nitrate compound which is employed may vary considerably. 'For themost eflicient operation using nitrates as the oxidizing agent it hasbeen found that it is desirable to use from about 2% to maximumsolubility of the nitrate compound and preferably from 2% to of nitratecompound calculated on an N0 basis, although the maximum amount will belimited by the solubility content.

Any leaching solution having the required oxidizing characteristics andsufliciently acidic to attack magnesium metal, may be suitably employed.Preferably, solutions of mineral acids such as nitric acid, hydrochloricacid and sulphuric acid are used in the leaching medium. Likewise,solutions containing other materials such as magnesium chloride and thelike which are also suiiiciently acidic to attack the metalliccontaminant may be included.

The concentration of the acidic solution which is employed may vary overa considerable range. However, for reasons of economy and ease ofoperation it has been found desirable to employ solutions which aredilute with respect to the presence of acidic constituents. For example,leaching solutions containing from about 2% to about 20% HCl have beensuccessfully employed. Chemical equivalent amounts for the other acidsmay also be employed successfully. When using some of the oxidizingagents, however, it has been found that concentrations other than thoserecited are more effective. Obviously highly concentrated acids shouldbe avoided for reasons of economy and to avoid other detrimentaleffects,

e. g. when using concentrated H 80 and HCl, the acid readily attacks thetitanium metal itself.

It has been found however that when nitric acid is used alone as theoxidizing agent that the corrosion effects including the effect on thetitanium metal itself are of much less importance, therefore nitric acidsolutions up to 70% concentration by weight of HNO may be advantageouslyemployed and it has been in fact discovered that such concentratedsolutions particularly when employed at elevated temperatures result ineffective suppression of hydrogen absorption by the metal. Employment ofsolutions containing less than 2% nitric acid will not providesufficient leaching action within a reasonable time to be economicallyfeasible. Therefore, the preferred range of concentration for nitricacid solutions to obtain the objectives of the invention is from about2% to about 70% concentration by weight of HNO Using highly concentratednitric acid has little corrosion effect on the titanium metal product.The actual loss by dissolution is immaterial in the process. Theconcentrated nitric acid has the advantage that the magnesium tilcontent of the impure sponge may be more readily and quickly dissolvedand the evolved hydrogen more efliciently taken care of. It isapparently helpful to provide suflicient reacting ions in the solutionto render the hydrogen innocuous so that it cannot enter or combine withthe titanium metal product. In the case of acid solutions containingnitrate salts the concentration which may be successfully employed isoften limited by the solubilities of the salts and by the practicalaspects of corrosion effects on the tanks and apparatus employed.

The combination of various acids and oxidizing agents is effective inproducing results in accordance with the objects of this invention.Under certain circumstances combinations of certain acids and salts maybe considerably cheaper than the use of relatively expensive mtric acidalone, and may be more available and more conveniently handled in plantpractice. In either case the titanium metal produced as amenable to arcmelting and selection of the particular reagents employed will dependupon conditions. It is obvious that the specific quantity of agents tobe employed in any particular operation Will depend upon a variety offactors such as for example, the amount of contamination which may bepresent, the physical form of the titanium metal product to 'bepurified, the size of the equipment, etc.

The reason why the presence of an oxidizing agent in the acid leachingsolution results in an improved titamum metal product with respect tosubsequent processing op erations is not presently clear. It ispostulated that the oxidizing agent reacts with hydrogen gas which maybe evolved during the leaching operation and thereby prevents suchgaseous material from being absorbed by the titanium product, or it maybe that the oxidizing agent itself is reduced in preference to hydrogenand that its reduced products are not absorbed or occluded by thetitanium metal.

The leaching operation maybe conducted over a rather wide temperaturerange. For effective removal of the impurities it has been foundsuitable under most conditions to initiate the leaching operation atessentially room temperature. Normally an evolution of heat willaccompany the leaching operation, but the resulting temperature increaseappears to produce no ill effects.

In order to illustrate the instant invention more clearly, the followingexamples are presented:

Example 1 70 parts of a sample of coarse titanium metal which wasprepared by the reaction between titanium tetrachloride and moltenmagnesium metal by a process similar to that disclosed by Kroll in U. S.Patent No. 2,205,854 for producing titanium meta-l and which wascontaminated with a quantity of magnesium metal and magnesium chlorideWere subjected to a leaching operation. 1460 parts of an acidic solutioncontaining 44 parts H 50 and 292 parts NaClO were employed as theleaching medium. These amounts correspond to -a concentration of 3% H 50and 20% NaClO The acid was added slowly during the first one-half hourof the leaching operation. The leaching operation was continued for aperiod of four hours at temperatures of between about 24 C. and 47 C. Atthe end of the leaching period the titanium metal was removed from theacid leaching solution containing the NaClO and was washed with waterand dried for a period of about three hours at a temperature of about C.Substantially all of the magnesium and magnesium chloride were removedby this operation. After the contaminants had been removed and theproduct dried, the titanium metal product was then transferred to an arcmelting apparatus and melted, and the molten titanium was subsequentlycast into ingot. form. The titanium metal ingot possessed a Brinellhardness number of 220. During the arc melting operation there was nodifficulty in maintaining astable arc, and there was prac- -thesolution.

daily no spattering ofthe titanium metal as it was being melted.

Example 2 The same amount of another portion of the impure titaniummetal employed in Example 1 was subjected to another acidic leachingoperation in order to remove contaminating magnesium metal and magnesiumchloride. The acidic leaching solution in this example consisted of 1500parts of solution containing 150 parts H 80 and 150 parts KMnO Theleaching operation was continued for a period of four hours attemperatures of between about 34 C. and about 44 C. The leachingoperation and subsequent are melting and casting steps were conducted inthe manner described in the preceding example. Once again no difiicultywas experienced during the arc melting step, and the cast ingot hadBrinell hardness number of 140.

Example 3 Example 4 The process described in Example 1 was repeatedexcept 1500 parts of solution containing 45 parts of HCl and 45 parts ofK Cr O were used. Again the titanium metal was arc meltedsatisfactorily.

Example 5 Another portion of an impure titanium metal of the type usedin the preceding examples was treated as described in Example 1 except1600 parts of a solution containing 180 parts of TiCl were used. Againthe contaminants were removed, and satisfactory arc melting wasrealized. The ingot produced had a Brinell hardness of 140.

Example 6 The process described in Example 1 was repeated except 1400parts of a solution containing 140 parts of H 50 and 84 parts of K wereemployed. The results obtained were similar to those previouslydescribed, and ingot Brinell hardness was 137.

Example 7 Another portion of impure titanium metal of the type used inthe preceding examples was treated as described in Example 1 except 1200parts of a solution containing 36 parts of HCl and 180 parts of SnClwere employed. The titanium metal surface was coated with a depositwhich was subsequently easily removed by leaching in dilute acid. Thetitanium metal was then are melted satisfactorily.

Example 8 Another portion of impure titanium metal was placed in 900parts water and chlorine gas was bubbled through The treated titaniummetal was then are melted satisfactorily.

Example 9 Example 10 The process described in Example 1 was repeatedexcept 1500 parts of an acidic solution which contained 150 parts HCland 117 parts NaNO were employed in this operation. These amountsrepresent about 10% HCl and about 5.7% HNO The leaching was continuedfor a period of 4 hours at temperatures generally between 20 C. and 60C. At the end of this time the titanium metal was removed from theacidic leaching solution, washed with water and finally dried for aperiod of three hours at a temperature of about 150 C. The resultsobtained were similar to those previously described and satisfactory arcmelting was realized.

Example 11 70 parts of a sample of titanium metal such as described inExample 1 were likewise subjected to a leaching opera tion in which anacidic leaching solution was employed. 1500 parts of the acidic leachingsolution containing 300 parts H 50 and 225 parts NaNO were used for thisoperation. These amounts represent approximately 20% H 50 and about 14%NaNO The leaching operation and subsequent arc melting and ingot castingsteps were conducted just as was described in the preceding examples.Once again no difiiculty was experienced during the arc melting step andthe cast ingot had a Brinell hardness number of 175.

Example 12 Example 13 Contaminated titanium metal of the type used inthe preceding examples was leached with 65% nitric acid solution'andsubstantially identical results were obtained except that the leachingoperation was conducted in substantially one-half the time required forleaching the titanium metal using weaker or more dilute solutions.

Example 14 In this example contaminated titanium metal was leached witha solution containing 35% sulphuric acid and 10% sodium nitrate. Resultssimilar to those recorded in'Example 11 were obtained.

Example 15 Contaminated titanium metal was leached with 1500 parts of asolution containing 420 parts of HCl and 300 parts of FeCl This solutionis equal to about 28% HCl and 20% FeCl Again good quality metal wasobtained after a subsequent satisfactory arc melting operation.

Example 16 Another portion of the impure titanium metal was subjected toan acidic leaching operation. The acidic leaching solution in thisexample consisted of 1500 parts of solution containing 75 parts H and 75parts FeCl These amounts correspond to a concentration of about 5% H 80and about 5.0% FeCl Once again no difficulty was experienced during thearc melting step, and the cast ingot had a Brinell hardness number of204.

Example 17 Still another portion of the impure titanium metal employedin the preceding examples was subjected to a leaching operation in orderto remove the contaminating.

leaching solution consisted of 1500 parts of a 15% ferric chloride.solution. This leaching solution was sufliciently acidic to attack themagnesium metal and thus remove it from the. titanium metal product. Theseparated titanium metal product was subsequently washed and dried andwas then processed by an arc melting operation, and the are proved to bevery stable. The titanium metal ingot which was formed possessed aBrinell hardness of 210.

Similar results to those described. in the above examples also wereobtained using ozone, bromide and Na CrO chromic acid, MnO PbO NaClQNaClO, KBrO and CuSOr. a

For comparative purposesand in order to illustrate the effectiveness ofthe instant invention two other portions of the impure titanium metalproduct employed in Example 1 was subjected to leaching operations inwhich one portion was treated with the. same amount. of sulfuricacidl'eaching solution as was employed in Example 1 and the otherportion was treated with the same amount of hydrochloric acid leachingsolution as was employed in Example 10. However, no oxidizing agent wasemployed in either case. Although apparently the contaminants, includingmagnesium metal and magnesium chloride were removed'in both leachingoperations the titanium metal product could not be suitably employed ina subsequent arc melting operation inasmuch as there was excessivespattering of the titanium metal, and furthermore, it proved impossibleto maintain a stable arc during the melting operation.

It has clearly been demonstrated by the examples presented and bythepreceding description that according to the process of the instantinvention, it is possible to effectively remove contaminants such as,for example, magnesium metal and magnesium chloride from titanium metalby a leaching operation in which the acidic leaching solution contains.an oxidizing agent. The products resulting from such leaching step areparticularly amenable to a subsequent arc melting operation.Furthermore, it has been shown that it is possible to accomplish suchremoval by a leaching operation which is simple and economical to employand which does not require complex equipment or large amounts ofadditional purifying agents.

Asset out above, the instant application is a continuation-in-part ofour applications Serial Nos. 365,776, 365,777 and 365,778, all of whichwere filed July 2, 1953, and expressly abandoned on April 27, 1955;application Serial No. 365,776 being a continuation-in-part of anearlier application Serial No. 297,996 filed July 9, 1952, nowabandoned; application SerialNo. 365,777 being a continuation-in-part ofan earlier application Serial No. 293,660 filed June 14, 1952, nowabandoned; and application Serial No. 365,778 being acontinuation-in-part of an application Serial No. 326,352 filed December16, 19 2 now. a and ne While this invention has been described'andillustrated by. the examples shown, it is not intended to be strictlylimited thereto andother modifications may be employed within the scopeof the following claims.

We claim:

1. A process for removing the reaction byproducts from crude unleached.titanium metal produced by reduction from its halide and for preventingabsorption of hydrogen in the titanium metal product during removal ofsaid reaction byproducts which comprises admixing said crude metal withan oxidizing acidic solution to solubilize the reaction byproducts fromsaid metal and separating said solution containing the solubilizedreaction byproducts from. said titanium metal, said oxidizing ac d ol tnv apab Qt xid zi y tq sn as. o his drogen ion.

2. A process for removing the reaction byproducts from crude unleachedtitanium metal produced by reduction from. its. halide. and. forpreventing. absorption of hydrogen in the titanium metal: product.during: re: moval of said reaction byproducts: which comprises ad.-.mixing said crude metal with an oxidizing acidic solution to solubilizethe reaction byproducts from said metal and separating said solutioncontaining the solubilized reaction byproducts from said titanium metal,said oxidizing acid solution selected from the group consist-- ing of;nitric acid, an acid. solution containing a salt se-. lected from thegroup consisting of nitrate and ferric iron, and an acid solutioncontaining a gas dissolved therein selected from the group consisting,of chlorine. and oxygen.

3. A process for removing the reaction byproducts from crude unleachedtitanium metal produced by reduction from its halide and for preventingabsorption of hydrogen in the titanium metal, product. during removal ofsaid reaction byproducts which comprises admixing said crude metal withan oxidizing acidic solution to solubilize the reaction byproducts fromsaid metal and separating said solution containing the solubilizedreaction. byproducts from said titanium metal and washing said titaniummetal product, said oxidizing acid solution selected from the groupconsisting of nitric acid, an acid solution containing a salt selectedfrom the group con.- sisting of nitrate and ferric iron, and an acidsolution containing a gas dissolved therein selected from the groupconsisting of chlorine and oxygen.

4. Method. according to claim 2 in which said oxidizing acid solution isnitric acid.

5. Method according to claim 2 in which said oxidizing acid solutioncontains sodium nitrate.

6. Method according to claim 2 in which said oxidizing acid solutioncontains ferric chloride.

7. Method according to claim 2 in which, said oxidizing acid solutioncontains chlorine gas.

I 8. Method according to claim 2 in which said oxidizing acid solutioncontains oxygen gas.

References Cited in the file of this patent UNITED STATES PATENTS1,602,542 Marden Oct. 12, 1926 1,814,719 Marden et al July 14, 19312,274,237 Jaeger et a1 Feb. 24, 1942 2,299,228 Gray et al. Oct. 20, 19422,546,933 Steahly et a1. Mar. 27, 1951 2,697,660 Sibert Dec. 21, 1954OTHER REFERENCES American. Inst, of Mining and Metallurgical Engineers,TechnicalPublication No. 1961 (19.46), pages 5, 7 and8.

Systematic Inorganic. Chemistry, by Caven. et al., 6th ed'., published.in 1946. by Blackie & Son. Ltd., London. Pages 142, 143., 147 and148.

Titanium, Report ofv Symposium, pub. December 16, 1948, by Ofiice ofNaval Research, D. C., page 81.

Product Engineering, vol. 20, No. 11, November 1949, page 142.

A Dictionary of Chemical Equations, by Gilman; pub. in 1950 by ElectricPublishers, Chicago; page 80.

The Making, Shaping and Treating of Steel, by Camp et al., 6th. ed.,published in 1951 by U. S. Steel Co., Pittsburgh, Pa., page 879.

Inorganic Chemistry, by Moeller, pub. in 1952 by John Wiley & Sons,Inc., New York, pages 411-412.

1. A PROCESS FOR REMOVING THE REACTION BYPRODUCTS FROM CRUDE UNLEACHEDTITANIUM METAL PRODUCED BY REDUCTION FROM ITS HALIDE AND FOR PREVENTINGABSORPTION OF HYDROGEN IN THE TITANIUM METAL PRODUCT DURING REMOVAL OFSAID REACTION BYPRODUCTS WHICH COMPRISES ADMIXING SAID CRUDE METAL WITHAN OXIDIZING ACIDIC SOLUTION TO SOLUBILIZE THE REACTION BYPRODUCTS FROMSAID METAL AND SEPARATING SAID SOLUTION CONTAINING THE SOLUBILIZEDREACTION BYPRODUCTS FROM SAID TITANIUM METAL, SAID OXIDIZING ACIDSOLUTION CAPABLE OF OXIDIZING HYDROGEN GAS TO HYDROGEN ION.